Accurate and effective fault diagnosis of high-voltage transmission line （ FDHVTL） is vital for the rapid restoration,as well as for maintaining the security and reliability of the power systems concerned. In this paper,the FDHVTL is formulated as an optimization problem with the fault location,fault type identification and fault time estimation involved. Then,by setting the variables to be solved （ such as the fault location） and the parameters to be determined （ such as the transition resistance） as the unknown parameters in a fault hypothesis,and the minimum discrepancy degree between the actual and the expected waveforms as the optimization objective. Then,a hybrid optimization model with discrete and continuous variables is established and solved with a heuristic optimization algorithm,i. e. ,the harmony search （ HS） algorithm. Some improvements of the HS algorithm are made next. Finally,it is demonstrated by sample results that the proposed method is correct and effective.